docs: improve README project architecture section (#45)

[Itodo-S]

Summary

Closes #45.

The README explained NotifyChain at a high level but did not describe how the smart contracts and off-chain services actually interact — and it still labelled the listener as a "future" component even though it is now implemented. This PR brings the architecture documentation in line with the current codebase.

Changes

• Architecture overview: added a three-layer overview (smart contracts, listener service, dashboard) with a component/responsibility table.
• Component interaction: added an ASCII diagram showing how on-chain events flow into the listener and out to Discord, the events API, and the dashboard, plus a reference to the detailed Documents/Task Bounty/ARCHITECTURE.md.
• Contract responsibilities: clarified that the on-chain layer is the source of truth and emits the typed events the off-chain layer consumes.
• Notification flow: added an end-to-end walkthrough (invoke → emit → poll → validate/register → deduplicate → notify → dashboard) and listed the key off-chain modules (EventSubscriber, NotificationDeduplicator, DiscordNotificationService, events API).
• Project structure: documented the previously-undocumented listener/ and dashboard/ directories.
• Features / tech stack: removed stale "coming soon / future" markers now that the listener service and Discord notifications exist.

Acceptance criteria

• README provides a clear system overview
• New contributors can understand component interactions
• Documentation remains concise and easy to follow

Documentation-only change; no code paths affected.

[Abd-Standard]

please fix CI

[Itodo-S]

Thanks for the review! I've rebased onto the latest main and pushed fixes for the failing CI. The failures were pre-existing on main, not from the README change:

Frontend (lint, typecheck, test)

• dashboard/package-lock.json was corrupted (invalid JSON in several places), which broke the Setup Node cache step and npm ci. Regenerated a valid lockfile.
• Added the @testing-library/jest-dom side-effect import to EventFiltersBar.test.tsx so toBeInTheDocument is typed during tsc --noEmit (the build step).

Rust (fmt check, tests)

• Ran cargo fmt on version_test.rs (import ordering) to satisfy the Check formatting step.

Verified locally:

• dashboard: npm ci ✅, npm run lint ✅, npm run build ✅, npm test ✅ (7 tests)
• contract: cargo fmt --all -- --check ✅ clean, cargo test --workspace --all-features ✅ (86 tests)

The new CI run is currently in action_required (awaiting maintainer approval to run workflows on a fork PR) — could you approve it when you get a chance? 🙏 @Abd-Standard